The present invention relates generally to apparatus and methods for conditioning inlet air for use in an aircraft cabin and, more particularly to apparatus and methods for conditioning cabin air while capturing and reusing energy that would otherwise be waste.
In aircraft operating in atmospheres with low pressure it is necessary to condition the cabin air to increase pressure and provide temperature and humidity control.
U.S. Pat. No. 6,250,097 shows a combined 4 wheel air cycle and liquid cycle system used to cool aircraft cabin air and avionics while recovering some heat energy in the process. In '097, an air cycle includes, inlet air from an aircraft turbine cooled by ambient air, compressed and cooled again by ambient air. The inlet air is then cooled again by use of reheat heat exchangers which route the warm moist inlet air over cooled inlet air downstream in the system. The inlet air is then expanded through a first turbine and water is extracted. The inlet air then enters an air to liquid heat exchanger where warm fluid containing heat energy from a liquid cycle used to cool the aircraft avionics is used to warm the inlet air. Then the inlet air passes through a reheater to gain energy from the next inlet air and is then expanded through a second turbine. The cool inlet air from this turbine is again warmed by the liquid cycle in a heat exchanger and the air is then supplied to the cabin. This arrangement recaptures some of the available energy from the heat of vaporization of the liquid from the air and from reject heat contained in the liquid cycle from aircraft avionics. However, '097 does not disclose a way to continue to cool the aircraft avionics when the avionics heat energy is not needed in the air cycle. Aircraft electronics and avionics must be cooled constantly or they will overheat. Therefore there must be a way to cool the avionics even when the waste energy is not needed. In operation, there are also conditions when it would be desirable to at least partially bypass some elements of an air conditioning system. For example, at high altitude operation when ambient air is cool and dry relative to cabin conditions, the first turbine in air cycles such as that shown in '097, is not needed. The first turbine has a smaller nozzle intake and therefore constricts flow more than the second turbine so the system shown in '097 bleeds air off the aircraft turbine engine that is not required to condition cabin space, wasting energy.
Another prior art example of the so-called 4-wheel environment control systems is shown in Warner U.S. Pat. No. 5,086,622. The Warner patent figure shows a bypass valve 72 that bypasses the first turbine during high altitude aircraft performance when the turbine would not be needed. For example, during high altitude performance, when ambient air is cooler and bleed air is less humid than at ground level, operation of the first turbine would waste energy by drawing un-needed bleed air from the turbine engine. The inefficient operation of Warner forces designers to build the system components, particularly heat exchangers, larger than needed which in turn wastes more aircraft fuel in carrying the additional weight.
As can be seen, there is a need for an improved condensing cycle energy recovery system that is compact and economical to operate. There is a need for an improved apparatus and method for condensing cycle energy recovery system that makes use of all energy available, including waste energy from aircraft avionics. There is further a need for a condensing cycle energy recovery system that is efficient so that system components can be sized as small as possible and still do the job of conditioning the aircraft cabin space.